I typically pick up about 10% on speed when I ride my Tri vs. my road... on a sprint distance... under 20 miles, you might save a couple minutes. Yes, it will help, but probably not $2000.00 worth. It MAY also help your run a bit by changing the muscles that you use on the ride... how much? Not likely to be more than another minute or two (on 5k?)... From a purely financial standpoint, its difficut to justify.

HOWEVER... when you come to terms with the hobby that you have selected (cycling), like I have, you allow yourself a bit of leeway... I LOVE (LOVE LOVE LOVE) riding my Cervelo P2... Its fast, I feel fast, it looks good, it takes weight off my wrists, it changes my leg position... well worth it!